U2010B_10 Datasheet, PDF (5/18 Pages) ATMEL Corporation – Programmable Load-current Limitation with Over- and High-load Output

U2010B
3.4 Automatic Retriggering
The current-detector circuit monitors the state of the triac after triggering by measuring the volt-
age drop at the triac gate. A current flow through the triac is recognized when the voltage drop
exceeds a threshold level of typically 40 mV.
If the triac is quenched within the relevant half-wave after triggering (for example owing to low
load currents before or after the zero crossing of the current wave, or for commutator motors,
owing to brush lifters), the automatic retriggering circuit ensures immediate retriggering, if nec-
essary with a high repetition rate, t_pp/t_p, until the triac remains reliably triggered.
3.5 Current Synchronization
Current synchronization fulfils two functions:
– Monitoring the current flow after triggering.
In case the triac extinguishes again or does not switch on, automatic triggering is
activated until the triggering is successful.
– Avoiding triggering due to an inductive load.
In the case of inductive load operation, the current synchronization ensures that in
the new half wave, no pulse will be enabled as long as there is a current available
from the previous half wave, which flows from the opposite polarity to the actual
supply voltage.
The current synchronization as described above is a special feature of the U2010B. The device
evaluates the voltage at the pulse output between gate and reference electrode of the triac. As a
result, no separate current synchronization input with specified series resistance is necessary.
3.6 Voltage Synchronization with Mains Voltage Compensation
The voltage detector synchronizes the reference ramp with the mains supply voltage. At the
same time, the mains-dependent input current at pin 15 is shaped and rectified internally. This
current activates the automatic retriggering and at the same time is available at pin 5. By suit-
able dimensioning, it is possible to obtain the specified compensation effect. Automatic
retriggering and mains voltage compensation are not activated until ⏐ V_{15 - 10}⏐ increases to 8 V.
The resistance R_sync. defines the width of the zero voltage cross over pulse, synchronization cur-
rent, and hence the mains supply voltage compensation current.
Figure 3-1. Suppression of Mains Voltage Compensation and Automatic Retrigger
Mains
R2
2x
C6V2
15
U2010B
10
If the mains voltage compensation and the automatic retriggering are not required, both func-
tions can be suppressed by limiting ⏐ V_{15 - 10}⏐ ≤ 7 V, see Figure 3-1.
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